Baboons Shed Light on Human Brain Evolution

Baboons Shed Light on Human Brain Evolution

Research with baboon brains has provided new insight into the evolution of the human brain, a new study contends.

The genetics behind the development of folds in the human brain have been a mystery, but there are new clues in a study scheduled for presentation Sunday at the annual meeting of the Society for Neuroscience, in San Diego.

As the human brain evolved, there was a dramatic increase in the number of brain cells and connections, the researchers said. But this growth was restricted by the size of the skull in relation to the birth canal, leading the brain to fold into ridges and valleys.

“The evolution of the human brain over time is a very complex process,” Elizabeth Atkinson, of Washington University in St. Louis, said in a Society for Neuroscience news release. “Our study connects the folding of the brain with the underlying genetics, and provides unique insight into how the evolution of our genes has driven the shape, and ultimately the function, of our brains.”

4 COMMENTS

Google Image “dolphin brain”. It too has folds, but it is much less spherical. I would guess dolphins have less problem with heads fitting through the birth canal. I was present at a dolphin birth. It was much quicker and apparently less traumatic than a human birth. So in the dolphin at least, folding may have occurred without evolutionary pressure of the small birth canal.

The largest brains are those of sperm whales, weighing about 8 kg (18 lb). An elephant’s brain weighs just over 5 kg (11 lb), a bottlenose dolphin’s 1.5 to 1.7 kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg. Humans dismiss this by bringing in body weight. A dinosaur needed only a walnut sized brain to control its body. Large animals do not have extra muscles. They have greater surface area with sensory cells, but I find it ridiculous a sperm whale would develop such a huge brain solely for that purpose.

Sonar processing for the whales and dolphins would take up much of the large brain. But that does not explain the elephant.

Neuron and synapse count are the most likely indicator of brain functional sophistication. Indeed, the lists here are mostly sequenced per our expectations.

Cells are size constrained by a surface area to volume requirement. The surface area maps to a rate of nutrient absorption. Nominally round cells tend to optimise at 10 to 20 microns in every animal, so bigger animals will have more such cells. Long thin cells, though can become arbitrarily large through becoming longer. Neurons fit this bill. The ratio of the known neuron count and the brain mass would suggest much larger/longer brain cells exist in these larger animals, though additionally, these elongated cells will presumably need much better insulation/myelination to ameliorate transmission delays and losses, hence much more fat in the white matter also bulking things up.

It is interesting to note that whales also have spindle cells (or Von Economo cells, think broadband data channels) which, in humans are used to speed high level inferences from the cortex back down to more primitive levels. (For us they allow an opportunity to veto gut reactions, in time, say, to avoid a needless death when a small child helpfully opens the blinds unaware of your hangover). The big long cells in whale brains may need such speedy help for simpler functional reasons.

The size of ancient humans brains had already increased much larger than chimps but its interesting that it has 30 % more folds than chimp brains…
Is this a consequence of the human skull reaching the maximum size it could be in order to fit through the birth canal and pelvic opening ?…
Didn’t ancient humans also need to forgo several months of extra gestation in the womb because our brains and skull size were too big to fit through the pelvis – so it was either be born earlier at 9 months – under developed and more dependant for longer……Or risk our skull growing too big to be born at a more developed stage…
Is that why human brains have more folds to compact them for birth and allow expansion later ? and maybe our skulls coped with the size increase by being soft and incomplete at birth later hardening and sewing up at the crown………Human brain/ skull expansion seems to be evolving faster than the pelvis can adapt to…